Deep Brain Stimulation (DBS) has been found to be successful in treating a variety of brain-controlled disorders, including movement disorders. Generally, such treatment involves placement of a DBS type lead into a targeted region of the brain through a burr hole drilled in the patient's skull, and the application of appropriate stimulation through the lead to the targeted region.
Presently, in DBS, beneficial (symptom-relieving) effects are observed primarily at high stimulation frequencies above 100 Hz that are delivered in stimulation patterns or trains in which the interval between electrical pulses (the inter-pulse intervals) is constant over time. The trace of a conventional stimulation train for DBS is shown in FIG. 2. The beneficial effects of DBS on motor symptoms are only observed at high frequencies, while low frequency stimulation may exacerbate symptoms See Benabid et al. 1991, Limousin et al. 1995. Thalamic DBS at less than or equal to 50 Hz increases tremor in patients with essential tremor. See Kuncel et al. 2006. Similarly, 50 Hz DBS produces tremor in pain patients receiving simulation of the ventral posterior medial nucleus of the thalamus (VPM), but the tremor disappears when the frequency is increased. See Constantoyannis 2004. Likewise, DBS of the subthalamic nucleus (STN) at 10 Hz worsens akinesia in patients with Parkinson's disease (PD), while DBS at 130 Hz leads to significant improvement in motor function See Timmermann et al. 2004, Fogelson et al. 2005. Similarly, stimulation of the globus pallidus (GP) at or above 130 Hz significantly improves dystonia, whereas stimulation at either 5 or 50 Hz leads to significant worsening. See Kupsch et al. 2003.
Model studies also indicate that the masking of pathological burst activity occurs only with sufficiently high stimulation frequencies. See Grill et al. 2004, FIG. 1. Responsiveness of tremor to changes in DBS amplitude and frequency are strongly correlated with the ability of applied stimuli to mask neuronal bursting. See Kuncel et al. 2007, FIG. 2.
Although effective, conventional high frequency stimulation generates stronger side-effects than low frequency stimulation, and the therapeutic window between the voltage that generates the desired clinical effect(s) and the voltage that generates undesired side effects decreases with increasing frequency. Precise lead placement therefore becomes important. Further, high stimulation frequencies increase power consumption. The need for higher frequencies and increased power consumption shortens the useful lifetime and/or increases the physical size of battery-powered implantable pulse generators. The need for higher frequencies and increased power consumption requires a larger battery size, and frequent charging of the battery, if the battery is rechargeable.